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Numerical simulations of sawtooth activity in Tokamaks have been carried out using reduced magnetohydrodynamics (MHD) and a simple transport model. The electron temperature is evolved self-consistently including ohmic heating and a strongly anisotropic thermal conductivity. The character of the sawteeth is found to be sensitive to the values of the transport coefficients. In particular, a perpendicular viscosity V of the same order as, or larger than the perpendicular heat conductivity X, is needed to produce distinct relaxation oscillations. To study the region of high S, V and X were scaled as 1/S and only S was varied. The collapse time shows a much weaker dependence on S than the expected S(1/2) scaling, because the deviation of central q away from 1 over the sawtooth cycle decreases for increasing S. Furthermore, the resistive instability is turned on quickly because the shear changes from almost zero in the central region to order unity over one resistive layer width. The sawtooth period and collapse time simulated for S < 1.0 E7 compare favourably with those observed in small tokamaks. At S = 1.0 E7, the collapse time is close to that observed in the Frascati Tokamak (FT), but the period is somewhat too short.

Additional information

Authors: VLAD G, ENEA, Centro Ricerche Energia Frascati, Roma (IT);BONDESON A, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: Paper presented: Theory of Fusion Plasmas, Chexbres (CH), Oct 3-7, 1988
Availability: Available from (1) as Paper EN 34469 ORA
Record Number: 198910513 / Last updated on: 1994-12-01
Original language: en
Available languages: en